This invention relates generally to pipe supports or hangers and, more particularly, to a spring hanger designed to support a pipe while permitting vertical movement thereof due, for example, to thermal expansion and contraction of the pipe or other pipes of a piping system.
A conventional spring hanger comprises a cylindrical casing closed at its upper end by an end head or cover plate, and a coil compression spring inside the casing held compressed between a backing plate (referred to in the trade as a "piston" plate) adjacent the upper end of the casing and a reaction ring adjacent the lower end of the casing. A support rod connected at its upper end to an I-beam, for example, is threaded at its lower end into the upper end head of the casing for suspending the spring hanger from the beam. The upper end of a second rod is threaded up into a piston rod (referred to in the trade as a "turnbuckle") which extends vertically inside the casing down from the piston plate through the coil spring and reaction ring. A pipe clamp is carried at the lower end of this rod for supporting a pipe. When the hanger is subjected to a load, the piston plate moves down in the casing to compress the spring.
Heretofore, the reaction ring, against which the lower end of the coil spring bears, has been held in position relative to the spring casing in various ways, all of which have proven to be less than satisfactory. For example, the ring has been welded directly to the casing, but this destroys the galvanized finish of the parts, causing corrosion problems. The ring has also been supported by an underlying ring bolted to the casing. However, this arrangement is disadvantageous in that the bolts tend to loosen over time and to corrode. A snap ring received in an annular internal groove in the casing has also been used to retain the reaction ring in place, but such a groove substantially weakens the casing wall, especially where the casing is out-of-round.
Another problem associated with spring hangers has involved locking the piston plate at a selected axial (vertical) position within the spring casing. In this regard, a spring hanger is typically preloaded to a "design" load prior to installation by forcing the piston plate down a predetermined distance to compress the coil spring. The magnitude of this "design" load is calculated to be as close as possible to the actual (or "live" load) to be supported by the hanger when installed. After the hanger has been preloaded, the piston plate is mechanically locked in position relative to the casing, the hanger shipped to the place of installation and installed, the pipe clamped in place on the hanger at the proper pipe elevation, and the piston plate then released relative to the casing to transfer the live load of the pipe to the coil spring. If the "design" load matches the "live" load, the pipe supported by the hanger will remain at the same elevation when the piston plate is released. If not, the pipe will move up or down. The hanger is then adjusted to bring the pipe back to its proper elevation.
Changes to a piping system supported by spring hangers are frequent due to the addition of new equipment, new piping, etc. In such cases, it is desirable to again lock the piston plate relative to the casing of the hanger until the changes have been completed.
Prior to the present invention, the various means for securing the piston plate relative to the casing after the coil has been preloaded have been less than satisfactory. For example, one such means has been to insert a retaining pin through aligned holes in the casing and the side edge of the piston plate. While this system may be workable for the initial installation of the hanger, it cannot subsequently be used since the holes usually move out of alignment when the pin is removed to transfer the "live" load to the coil spring. Other arrangements have also been used to lock the piston plate relative to the casing prior to and during the initial installation of the hanger, but all have had drawbacks and few have been capable of effective use after the intial installation of the hanger has been commpleted.
Reference may be made to U.S. Pat. Nos. 2,373,125, 4,176,185 and 4,238,102 for spring hangers and other devices relevant in a general sense to the present invention.